Audi Cabriolet 1998 2.6 revs bouncing help!

I had the issue on my Audi where the fuel and temp guage were temperamental... So I sorted that out but disconnected the battery first as had to remove airbag.

When I put the battery back on, it was low for some reason and car wouldn't start.

So I took the battery out and charged it at home.

Put the battery in and started the car and it started to idle very high until it finally dropped to 1,500 and started to bounce to 1,700 every second.

I've tried the idle reset by pulling ecu fuse and turning ignition for 5 seconds then off then start again but same thing... Revs constantly bouncing.

I've searched for vacuum leaks and none found. Tried vagcom (free version) and no error codes...

Any ideas?? Can someone help? MOT due in 2 weeks and it decides to do this 😣

VID_20181228_142340.mp4 - Google Drive

https://drive.google.com/file/d/1DWo...ew?usp=sharing

Here's a video of what it does... ok maybe not 1500-1700 bounce, more like a 1500-1550 bounce. When I'm driving, it's actually pulling the car forward without me touching the accelerator if the revs drop below 1500!!

Any help would be appreciated. :)

Hi , stay calm, it sorts itself out.
I also nearly ---- myself when I fitted a new battery to an ABC V6 coupe, which had sat flat for a while.
I was fitting the new battery prior to a potential buyer coming to view the following morning, and my car did exactly the same thing.
I read all the various methods for resetting throttle body and this and that but nothing made a difference.
I kept going out to the car and starting it up to see if anything had changed.
Eventually I decided to just let it run for 15 minutes and switch it off for 15 minutes, then repeat, and basically it calmed itself down after a couple of hours messing about and returned to normal on its own account.
I never found out what or why but had the very same issue with my ABC V6 cabby after flattening the battery from leaving the ignition and lights on for ages whilst I was working on the car.
I did pretty much the same thing, run for 15, off 15,on etc and it sorted itself out, still no wiser, have recommended this procedure to others and they had success.
The cars were 1996 ABC Coupe and 1997 ABC Convertible both v6 5 speed manual cars.
Good luck

Stuart

The ABC is a notoriously sensitive engine, disconnecting the battery deletes the learnt values in the ECU. Sometimes they will relearn the way the engine behaves away from the base map, sometimes they won’t such as when the idle valve is clogged up and they have to be set up using a diagnostic system and following a specific procedure to gain control of the idle.

Wow - cheers Stuart!!! I thought I had killed the car!! :D I searched everywhere and all I saw was either:

Option 1: Pull the ECU fuses for several minutes, turn ignition to on for 10 seconds, turn off, then start the car
Option 2: Turn ignition on for 30s, turn off, repeat and then start the car

I'll give it a go tomorrow. Have to replace the headlight switch first which means another battery pull as full beam and flasher isn't working hence that yellow warning sign on my dash. Been there since I bought the car 6 months ago and it was an advisory on the previous 2 MOTs. Hopefully the switch will resolve that and it's not something silly like the previous owner put the wrong bulbs in or something...

When you say run for 15 minutes do you mean drive it about or just let it sit there idling away for 15 minutes?

Thanks Crasher - I've already ordered a replacement idle valve if that is the culprit. It was running a bit rich recently but I thought that was because it was sat on previous owners drive for about 5 months when I bought it and just needed a good service.

If Stuarts advise doesn't resolve the issue, I may have to replace that valve. Or I may just replace it anyway :)

@fourringsrus Stuart

That sorted mine out!! Oh what joy to start the car and it stables at a low RPM :)

Mine wasn't strict 15 minute cycles. I tried the cycles for about 2 hours and then gave up. Came back to it 2 hours later and when I started it, it did it again. Drove it for 2 minutes, parked up to get something from shops. Came back to the car and it was stable! :)

Now I'll have to do that again soon as was sent the wrong indicator stalk!! Serves me right for ordering based on my reg rather than the part number off the part I guess :D

Last night after I replied,I searched back to see what I had stated during my first time with this issue and to be totally honest I dont think I was playing in strict 15 minute cycles, probably something similar to what you have done.
As Steve (crasher) states above, the ABC V6 can be a bit sensitive in set up procedures, but on the whole is a fantastic unit, possibly one of the best Audi produced.
Regarding doing it all again to change a headlight switch, I would not bother disconnecting the battery, but thats just me.
Glad you are sorted and good luck

Stuart

Cheers - unfortunately it's the headlight stalk that needs changing which means removing the steering and the airbag. Rather go through this hours of sorting the revs out than have an airbag explode in my face :D

Or is there a way I can supply power to just the ECU?